USB: gadget: AT91: fix typo in atmel_usba_udc driver

compile fix for bug introduced by 969affff547027)

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/atmel_usba_udc.c

@@ -2017,7 +2017,7 @@ static int __init usba_udc_probe(struct platform_device *pdev)
 			}
 		} else {
 			/* gpio_request fail so use -EINVAL for gpio_is_valid */
-			ubc->vbus_pin = -EINVAL;
+			udc->vbus_pin = -EINVAL;
 		}
 	}